There are heat exchangers comprising a casing surrounding a bundle of tubes through which a primary medium is flowed, a secondary medium being flowed through the casing surrounding the bundle of tubes for either heating or cooling by the medium flowing through the tubes of the tube bundle.
Often the primary medium flowed through the tubes of the tube bundle, is capable of fouling the insides of the tubes of the tube bundle, with time. The primary medium may be obtained from industrial waste water, public waterways and the like, and the fouling occurring on the insides of the tube bundle may be either mechanical deposits of sediment or deposits of salts or the like, particularly when the primary medium is a coolant liquid which removes heat from the secondary medium surrounding the outsides of the tubes of the tube bundle.
Fouling on the insides of the tubes of a heat exchanger is difficult to detect, and the degree of fouling is extremely difficult to measure, excepting that when there is inadequate heat exchange, the resulting trouble naturally leads to a suspicion that the heat exchanger tubes are fouled and possibly actually clogged.
Heretofore the practice has been to from time-to-time measure the thermal balance between the two mediums passing through the heat exchanger. Also it is, of course, possible to disassemble the heat exchanger for internal inspection of each tube of the tube bundle. Both expedients are time-consuming, put the heat exchanger out of operation, and are normally only resorted to when the heat exchanger fails to operate satisfactorily. Both expedients involve uncertainties and neither permits continuous monitoring of the heat exchanger's efficiency.